Growth and development studies over the past 200 years have demonstrated a so-called secular trend toward an earlier age of menarche in the industrialized world. Data also suggest larger increments of growth, greater size for age during childhood, and earlier final height attainment Despite questions about the reliability of past data collection methods, these trends appear to be accurate and the differences statistically significant. The age of menarche occurred 2-3 months earlier per decade during the past 150 years in Europe and the United States, with a leveling off of growth and age of menarche as standards of living increased More equitable socioeconomic conditions have also resulted in the elimination of discrepancies associated with social class and urban-rural differences. The current average age of menarche in the United States of 12.8 years has been relatively stable since 1947.